The influence of volition on breathing-swallowing coordination in healthy adults

This research was designed to clarify the role of cortical modulation in the coordination of respiration and swallowing. Time-locked recordings of submental surface electromyography, nasal airflow, and thyroid acoustics were used to evaluate nonnutritive breathing-swallowing coordination (BSC) and swallowing apnea duration (SAD) of 20 healthy adults during 3 conditions. These conditions represented a continuum of volitional through nonvolitional swallowing control on the basis of a decreasing level of cortical activation: voluntarily initiated swallows during wakefulness, nonvolitional awake swallows, and reflexively initiated swallows during sleep. Differing proportions of swallows at the cusps between inspiration and expiration were found between the volitional and nonvolitional conditions, irrespective of the level of arousal. SAD was unaltered by condition. In conclusion, BSC is influenced by degree of volition but not by level of arousal. This implies that cortical influence on BSC is limited to conditions in which swallowing is voluntarily initiated and indirectly implicates the recruitment of the supplementary motor or insular cortices. SAD remained stable across conditions and may therefore be considered relatively impervious to suprabulbar influence.